The present invention relates to a method for sawing a metal tube or hollow section using a band-saw machine, and to a band-saw machine for sawing a metal tube or hollow section.
A band-saw machine of the present type, which is used for the corresponding method, comprises a stationary lower saw part having a saw table for placing and fixing a metal tube or hollow section to be sawn, and an upper saw part which is movable in relation to the lower saw part and which has a revolving saw band which is equipped with a series of saw teeth and is driven in order to carry out a quasi-infinite sawing movement. By means of a feed motion of the upper saw part, which is performed in relation to the lower saw part, the saw band penetrates the metal tube or hollow section and, for performing a saw cut, is guided through said metal tube or hollow section.
Band-saw machines and methods of the type mentioned at the outset have been known for a long time, for example from DE 39 27 275 A1, from DE 198 28 589 A1, from EP 1 029 623 A1, or from DE 10 2013 210 573 A1. It is a common feature of these known band-saw machines that the workpiece to be sawn is placed on the saw table and fixed thereon, whereupon the upper saw part by means of a pivoting movement or of a linear movement is moved toward the lower saw part such that the driven saw band is also moved toward the workpiece until the saw teeth of said saw band penetrate said workpiece, and the saw cut is ultimately carried out. The saw cut is completed and the workpiece is fully severed when the saw teeth reach the plane of the saw table.
Since the upper saw part contains the blade drive for the revolving saw band, and the guide elements for the saw band, typically two or more wheels, by virtue of the high cutting forces during the saw cut have to be configured to be stable and solid, the upper saw part of a band-saw machine of the present type has a substantial weight. Therefore, it is typical for the feed motion to be generated substantially by the weight force of the upper saw part and for said feed motion to be regulated by decelerating measures. For example, if the upper saw part is lifted by means of hydraulic drives so as to prepare the band-saw machine for a new saw cut, the feed motion may be generated by bleeding the hydraulic oil from the hydraulic drives, wherein the movement may be regulated by throttling the volumetric flow of the hydraulic oil.
In the case of sawing metal tubes or hollow sections having a cylindrical or polygonal cross section, there is the issue that the saw shavings which are created during the saw cut to some extent drop into the interior of the metal tube or hollow section and are deposited there, in some instances accumulating in the course of the saw cut. When the saw band in the increasing progress of sawing then advances into that region of the metal tube or hollow section in which the dropped saw shavings lie, the latter may be entrained by the passing saw teeth of the saw band. Such entrained saw shavings may cause issues at that point where the saw teeth, having exited the interior of the metal tube or hollow section, again penetrate the wall of the latter, since said saw shavings upon re-entering the wall of the metal tube or hollow section are conjointly drawn into the cutting channel. On account thereof, the cutting surface on the metal tube or hollow section is significantly compromised, and the wear of the saw band is increased. In the case of saw teeth which are populated with cemented carbide tips, this may even lead to the cemented carbide tips breaking away.
Previous approaches to addressing this issue are based on continuous or periodic removal of saw shavings which have dropped into the interior of the metal tube or hollow section. To this end, for example a fluid, in particular an oil/water emulsion, is directed through the metal tube or hollow section, so as to wash out the saw shavings which have dropped therein. However, comparatively large amounts of fluid, which have to be made available and in particular to be collected, are required for this purpose, wherein band-saw machines are typically not conceived at least for the latter. The increased cleaning effort associated herewith and the provision of the fluid significantly increase the operating costs.
Another approach lies in continuously or periodically blowing out the shavings which have dropped into the interior of the metal tube or hollow section by the use of compressed air. Disadvantages are also not absent here, since there is the risk of saw shavings which have been blown out making their way into regions of the band-saw machine that are difficult to clean, or into regions which must be kept free of saw shavings. Depending on the length of the workpieces to be sawn, it is moreover difficult to deliver the compressed air to the location of the saw cut; since the compressed air has to be effective in the interior of the metal tube or hollow section, respectively, in some circumstances comparatively long lances which are correspondingly difficult to handle and to position are required.
Extraction of the shavings which have dropped into the interior of the metal tube or hollow section by suction has corresponding disadvantages, since here too a suction opening in the interior of the metal tube or hollow section has to be delivered to the location of the saw cut. Moreover, corresponding devices for generating a vacuum, and collection installations for the suctioned saw shavings, are required.
JP10058382 discloses a method for cutting a paper log in which a smooth blade band is used that does not include teeth, and instead utilizes a cutting edge to cut through the paper by raising the cutting band through the paper log. This provides a blade-type knife-cutting action so that there is no chip formation or removal during cutting of the paper. Toothed cutting bands cannot be utilized for cutting paper as the teeth would generate tear out and rips in the paper at the edges of the cut through the paper roll as well as the generation of chips/shredded paper, both of which are unacceptable.